Evaluation of PRKACA as a Therapeutic Target for Fibrolamellar Carcinoma

Background & Aims: Fibrolamellar carcinoma (FLC) is a rare, difficult-to-treat liver cancer primarily affecting pediatric and adolescent patients, and for which precision medicine approaches have historically not been possible. The DNAJB1-PRKACA gene fusion was identified as a driver of FLC pathogenesis. We aimed to assess whether FLC tumors maintain dependency on this gene fusion and determine if PRKACA is a viable therapeutic target. Methods: FLC patient-derived xenograft (PDX) shRNA cell lines were implanted subcutaneously into female NOD-SCID mice and tumors were allowed to develop prior to randomization to doxycycline (to induce knockdown) or control groups. Tumor development was assessed every 2 days. To assess the effect of treatment with novel selective PRKACA small molecule kinase inhibitors, BLU0588 and BLU2864, FLC PDX tumor cells were implanted subcutaneously into NOD-SCID mice and tumors allowed to develop. Mice were randomized to treatment (BLU0588 and BLU2864, orally, once daily) or control groups and tumor size determined as above. Results: Knockdown of DNAJB1-PRKACA reversed a FLC-specific gene signature and reduced PDX tumor growth in mice compared to the control group. Furthermore, FLC PDX tumor growth was significantly reduced with BLU0588 and BLU2864 treatment versus control (P = 0.003 and P = 0.0005, respectively). Conclusions: We demonstrated, using an inducible knockdown and small molecule approaches, that FLC PDX tumors were dependent upon DNAJB1-PRKACA fusion activity. In addition, this study serves as a proof-of-concept that PRKACA is a viable therapeutic target for FLC and warrants further investigation. ### Competing Interest Statement Stefanie S. Schalm is a current or former employee and shareholder of Blueprint Medicines Corporation; has a patent in conjunction with Blueprint Medicines Corporation. Erin O'Hearn is a current or former employee of Blueprint Medicines Corporation and Scorpion Therapeutics. Kevin Wilson is a current or former employee and shareholder of Blueprint Medicines Corporation, Foghorn Therapeutics, and Merck & Co. Timothy LaBranche is a current employee, leadership role and shareholder of Blueprint Medicines Corporation. Grace Silva is a current or former employee of Blueprint Medicines Corporation and Tessara Therapeutics; shareholder of Blueprint Medicines Corporation, Constellation Pharmaceuticals Inc., CytomX Therapeutics, Inc., Fulcrum Therapeutics Inc., Jounce Therapeutics Inc., and Kala Pharmaceuticals, Inc; received research funding from Blueprint Medicines Corporation. Zhuo Zhang is a current employee and shareholder of Blueprint Medicines Corporation. Lucian DiPietro and Neil Bifulco have patents in conjunction with Blueprint Medicines Corporation. Richard Woessner is a current or former employee of Onkur Therapeutics and Blueprint Medicines Corporation; shareholder of AstraZeneca and Blueprint Medicines Corporation; has patent in conjunction with AstraZeneca. Nicolas Stransky is a current employee of Celsius Therapeutics; shareholder of Blueprint Medicines Corporation and Celsius Therapeutics; and has patents in conjunction with Blueprint Medicines Corporation. Darshan Sappal is a current employee of Foghorn Therapeutics and shareholder of Blueprint Medicines Corporation. Robert Campbell is a current employee and shareholder of Blueprint Medicines Corporation. Riadh Lobbardi is a current employee of Blueprint Medicines Corporation; shareholder of Blueprint Medicines Corporation, Eyepoint Pharmaceuticals, Inc., Jounce Therapeutics, Magenta Therapeutics, Inc., Moleculin Biotech, Inc., Neon Therapeutics, and Surface Oncology, Inc. Michael Palmer is a current or former employee of Blueprint Medicines Corporation and C4 Therapeutics; shareholder of C4 Therapeutics, Magenta Therapeutics, and Sesen Bio; has a patent in conjunction with Blueprint Medicines Corporation. Joseph L. Kim is a current employee and shareholder of Blueprint Medicines Corporation; has a patent in conjunction with Blueprint Medicines Corporation. Chaoyang Ye is a current or former employee of Blueprint Medicines Corporation and NewCo Pharma Ltd; shareholder of Blueprint Medicines Corporation. Marion Dorsch is a current or former employee of Blueprint Medicines Corporation and NewCo Pharma Ltd; has leadership position in Blueprint Medicines Corporation, shareholder of Blueprint medicines Corporation. Christoph Lengauer is a current employee and shareholder of Blueprint Medicines Corporation and Third Rock Ventures; has leadership roles with Blueprint Medicines Corporation, Celsius Therapeutics, EQRx, Hookipa Pharma, Mersana Therapeutics, Inc., MOMA Therapeutics, Third Rock Ventures, and Exact Sciences; shareholder of Blueprint Medicines Corporation, Celsius Therapeutics, EQRx, Hookipa Pharma, Mersana Therapeutics, Inc., MOMA Therapeutics, Relay Therapeutics, Third Rock Ventures, and Exact Sciences; received honoraria from and had consulting or advisory roles with Bayer, Blueprint Medicines Corporation, Celsius Therapeutics, EQRx, Hookipa Pharma, Mersana Therapeutics, Inc., MOMA Therapeutics, Relay Therapeutics, Third Rock Ventures, Thrive Earlier Detection, and Exact Sciences; received expenses from Blueprint Medicines Corporation, Celsius Therapeutics, EQRx, Hookipa Pharma, Mersana Therapeutics, Inc., MOMA Therapeutics, Third Rock Ventures, and Thrive Earlier Detection, and Exact Sciences; has patents in conjunction with Blueprint Medicines Corporation, Celsius Therapeutics, Johns Hopkins University, and Thrive Earlier Detection. Timothy Guzi is a current or former employee of Blueprint Medicines Corporation and MOMA Therapeutics; shareholder of Blueprint Medicines Corporation; has patents in conjunction with Blueprint Medicines Corporation. Vivek J. Kadambi is a current or former employee and shareholder of Blueprint Medicines Corporation and Vertex Pharmaceuticals. Andrew Garner is a current or former employee of Blueprint Medicines Corporation and MOMA Therapeutics; shareholder of Blueprint Medicines Corporation. Klaus P. Hoeflich is a current or former employee and shareholder of Blueprint Medicines Corporation and Nested Therapeutics; and holds an advisory role with Turbine AI.